ACTION OF TISSUES. 105 



Krause (Algemeine U. Microscopische Anatomic, S. 74), 

 examines the osteoclasts very closely, and the manner in which 

 living bone is removed by them. He is of the opinion that 

 they furnish a secretion for this purpose, and thinks it con- 

 tains lactic acid. He says, ivory driven into the flesh is 

 absorbed by them, and that the osteoclasts are found in the 

 pits formed in it, as in living bone that is undergoing this 

 process; and quotes Kolliker, Billroth, De Morgan and 

 Tomes, as authority. These osteoclasts must be formed from 

 the ordinary connective tissue cells, or leucocytes. Not from 

 osteoblasts. 



ACTION OF TISSUES. 



Absorption under pressure is in no wise different from any 

 other process of absorption. A certain portion of the cells, 

 crowded, but not too much, take upon themselves a new 

 action and develop a ferment which destroys their neighbors 

 less favorably placed. It is well known that under pressure, 

 certain tissues are destroyed in preference to others. This 

 would be a very interesting field of research, but we have not 

 time to enter it in this lecture. 



This we conceive to be the normal action of the tissues of 

 the higher animals. How do the lower forms of life differ 

 from these? In the vegetative sense, the difference is but 

 slight. They differ widely in formative power. In the very 

 low forms the cells fall apart instead of aggregating and 

 unifying into more complex compound forms. In this sense 

 there is a wide physiological difference, but in the matter of 

 digestion, nutrition, and the formation of waste products, the 

 similarity is very close. 



